By Andy Cooke
The airship's natural home is in the sky. Free to follow the currents of the wind and air, roaming across the infinite blue. Yet, as with all aircraft, it must land eventually. Not only will it run out of fuel and other resources, its human crew are limited and need to recover to the land, sooner or later.
To do that, it will usually require ground facilities. The most important of these are mooring masts and sheds.
Sheds and mooring masts
An airship can land with no facilities or ground assistance, but this requires ideal conditions, otherwise it's a crash-landing (which could be fine, as long as fire doesn't break out. Should fire break out, you have the R101 crash - which crash-landed at under 13mph and fairly gently but then caught fire).
Of course, an airship with advanced technology could have more-easily vectored engines and widen the envelope of safe landing operations (the semi-rigid airship used in Beyond the Sunset is one such). If you are using airships for exploration and setting down routinely in bare sites, you'll probably need this (or a very casual attitude to risk).
Normally, however, you will need assistance on the ground (numbers depending on size of airship and facilities available), a mooring mast (preferably), and/or a shed.
A shed is simply an enormous hangar which you use to store your airship when not used. It should go without saying, but the Imperial Air Communications Conference in 1926 highlighted that: "Good ventilation is necessary to allow easy escape of hydrogen, and all electric fittings should be gas tight to prevent explosions."
The shed to be constructed by the Air Ministry at Karachi, on the far end of the proposed airship route to India, was to be 850 feet long, 180 feet wide, 170 feet high and able to withstand up to 35 pounds per square feet of wind pressure. If your airships are the size of OTL airships in the Twenties, that's the sort of scale you're looking at. You may go even larger, but then you're scaling up still further.
It can take a considerable number of people to manhandle an airship of any sort of size into the shed. This is, obviously, less than ideal (unless you happen to have a large surplus of people available). Then again, in some scenarios and potential timelines, the need for large numbers of semi-skilled people can be a positive.
If, however, you have a mooring mast, you need far fewer people.
The mooring mast evolved during WWI as part of an attempt to widen the useful operation envelope of airships (you needed low winds to get an airship into and out of a shed - for example, the R100 had only a few feet of clearance at the top and on each side, which meant that the slightest gust of wind could be highly dangerous when removing it from the shed or returning it into the shed).
Mooring masts weren't invented in the War, but they were was taken from their small, rudimentary pre-war incarnation through to their more established form in 1921.
The UK did lead the way in mooring masts, due to a deliberate choice by the Air Ministry. The eventual Cardington mast was the exemplar of the developed design: 200 feet high and 70 feet in diameter at the base. An elevator took passengers from the ground to the passenger platform, 170 feet up, and 40 feet in diameter (a stairway providing a backup).
The airship would drop a cable from the nose, which would be attached by ground crew to a cable coming out of the top of the steel turret on the top of the mast. This cable would be winched in, drawing down the airship until a cone on the nose locked into a bell-shaped cup on a telescopic arm, projecting out of the top of the mast and free to move in any horizontal direction and up to 30 degrees from the vertical. The arm would then be centred and locked (vertically), but free to swing horizontally, to allow the airship to move with the direction of the wind.
There was also a lower platform, 28 feet below the passenger platform, containing searchlights and signalling gear. The British intent was to be able to operate from the mast for long periods - refuelling and changing engines and even gasbags while moored at the mast. Fuel could be delivered at up to 2000 gallons per hour; water ballast at up to 5000 gallons per hour. The airship shed would, the intent was, then become more analogous to a dry dock than a harbour.
The mooring mast, in this incarnation, reduced the size of ground crew needed to as few as ten men - a huge manpower saving. However, they weren't universally used. While British-style masts did start to be used across the British Empire and in some allied countries, they weren't adopted by Germany - arguably the greatest airship user thanks to the Zeppelin company. They did not want to change their existing (proven) methods or pour in the capital investment; manpower was fairly cheap.
"Stub" masts, not much higher than half the diameter of the airship, as used eventually by the Zeppelin company, required far greater manpower. Lines dropped from the airship's nose were taken by up to sixty men (thirty each on port and starboard) and then shorter "spider lines" dropped on either side. Twenty men on each side pulled the airship down using the spider lines, whilst a further fifty would then take the rails on the outside of the control car. Twenty more would take the after car, and the 170 men would walk the airship to the stub mast, where it would be attached (It was possible to put the stub mast on wheels and use it to pull the airship into a shed).
The airship could then lower a gangway to the ground. This entire operation was arguably less potentially scary for the passengers, but significantly less efficient for operations.
In timelines where the PoD is pre-1920s, the mooring mast may have evolved differently. However, economics would be likely to drive efficiency over time, and mooring masts like the British design would eventually probably be seen world-wide - unless manpower remained cheap and/or easy (timelines where slavery remains or returns could see labour-saving technology stunted, for example, or timelines wracked with major recessions and depressions).
Further improvements and automation would be likely as technology became more advanced, such as telescoping mast spires for attachment and easy lowering (under control) of airships.
Airship Bases
So - where do you site your airship base? Given that many timelines will jut off from ours in this case at some point after the 1926 publication of "Approach towards a system of Imperial Air Communications: Memorandum by the Secretary of State for Air, laid before the Imperial Conference, 1926, together with the report of the Imperial Air Communications Special Sub-committee" (and timelines that split off before then will have usually had very similar constraints and airship developments), I'll let that answer the question:
"Selection of Site.
Whilst the linking up of commercial centres is the main object of high speed airship transport, there are certain operational factors which have to be borne in mind in selecting the precise site for an airship base and settling the type of base to be erected. A commercial airship will normally fly at a height above the ground of about 2,500-3,500 feet.
While there is no difficulty in flying higher than this, every 1,000 feet of height means a loss of about one-thirtieth of the total lift, and consequently diminishes the airship's carrying capacity.
It follows from this that a site for an airship base should be selected as nearly as possible at sea level, since, if an airship base is situated, say, 2,000 feet above sea level, the airship on levelling would have less useful lift for freight. For the same reason the base should, if possible, not be sited so as to necessitate flying over mountain ranges at the outset or in the early part of the journey, since the ascent can only be made by reducing the load of the airship which is uneconomic from the operating point of view.
On the other hand when an airship has been flying for some time and has thus used up a certain weight of fuel, an increase of height can be gained without the same loss of useful load. Due regard should also be paid to weather conditions, especially in choosing a site for a shed base with docking facilities, where an airship may have to be man-handled into the shed. They are not of so great consequence for an intermediate base with mooring mast only, as the airship would always be flown from the mast and not handled on the ground. At the same time local meteorological conditions might affect regularity of service; thus a locality in which thunderstorms are prevalent would generally be unsuitable.
...
In the immediate vicinity of a base there should be no obstruction such as hills, high buildings, etc., and any high masts for wireless telegraphy or meteorological purposes should be located as far as possible from the mast and shed, so as not to be a source of danger to an airship landing or leaving.
Local communications should be good to permit of passengers and freight being dealt with expeditiously. A main railway line should be in the vicinity. Feeder services by aeroplane should also be kept in view."
It also recommends that a minimum area of 600 acres (preferably up to 1000 acres) be available for the shed and mooring masts. However, for a base with just one mooring mast, "a clear space of about 800 yards square (about 130 acres) will suffice for a base with one mast provided there are no buildings of a greater height than 40 feet within 300 yards of the aerodrome. As the space required for landing operations at the mast is only about 100 acres, it is possible to use the remainder for grazing or other purposes. All electric cables in the vicinity of a base should be laid underground."
"Mooring Mast.
The existing type of mast consists of a steel structure 200 feet high, fitted with a receiving arm at the top to which the airship is anchored. The structure is built to withstand the pull of the airship up to 30 tons in any direction, in addition to a wind force on the structure of 30 lbs. per square foot. A lift is provided to convey passengers up and down the mast. Mains for hydrogen, water and fuel run up the mast for the replenishment of the ship, and are joined to similar mains in the ship by flexible connections.
The mast should be sited in such a position that an airship arriving or departing does not have to fly over the shed or other high buildings, and in any case these should be at least 800 to 1,000 yards away.
Anchor Points.
Twenty-four snatch block anchor points should be provided to take the sideguys when the airship is landing to the mast. These should be spaced in a circle round the mast at a radius of 750 feet from it, and should be designed to take a maximum pull of 25 tons in any direction. They should be placed flush with the ground to avoid obstruction.
A base would also need:
- Fuel storage
- Hydrogen Plant
- Power and Light
- Wireless Telephony
- Meteorological facilities.
The last should not ever be underestimated. As shown in the previous articles, the air meteorological conditions are always crucial to airship operation, and the importance of meteorological stations is underlined by the map included in that lengthy memorandum.
Your airship infrastructure will always be tightly interfaced with a meteorological system.
So - airship-wise, we have military airships, civilian airships, how they handle in the air and their navigation and weather concerns, and now the ground-handling elements. You have your alternate history airship - but how did your ATL still have them (or bring them back) when OTL lost them?
Next time: Potential PoDs.
Andy Cooke has written the sci-fi Endeavour trilogy (The End and Afterwards, Diamond in the Dark, Beyond the Sunset) and the political alternate history Lectern books (The Fourth Lectern, The Fifth Lectern), published by SLP